A fuel cell is an energy conversion device that converts chemical energy of fuel directly into electrical energy. That is, the fuel cell uses a fuel gas and an oxidizing agent, and adopts a method of producing electric power by using electrons generated during the redox reaction of the fuel gas and the oxidizing agent. A membrane-electrode assembly (MEA) of the fuel cell is a part in which an electrochemical reaction of hydrogen and oxygen occurs, and is composed of a cathode, an anode, and an electrolyte membrane, that is, an ion conductive electrolyte membrane.
A redox flow battery (oxidation-reduction flow battery) is an electrochemical power storage device that stores chemical energy of an active material directly into electrical energy by using a system in which the active material included in an electrolytic solution is oxidized and reduced and thus the battery is charged and discharged. A unit cell of the redox flow battery comprises an electrode, an electrolyte, and an ion exchange membrane (electrolyte membrane).
Fuel cells and redox flow batteries have been researched and developed as a next-generation energy source due to high energy efficiency and eco-friendly characteristics producing less emission of contaminants.
The most essential constituent element of the fuel cells and the redox flow batteries is a polyelectrolyte membrane capable of exchanging cations, and the polyelectrolyte membrane may have characteristics of 1) excellent proton conductivity, 2) prevention of crossover of the electrolyte, 3) strong chemical resistance, 4) strengthening of mechanical properties and/or 4) a low swelling ratio. The polyelectrolyte membrane is classified into fluorine-based, partial fluorine-based, hydrocarbon-based, and the like, and the partial fluorine-based polyelectrolyte membrane has a fluorine-based main chain, and thus has advantages in that physical and chemical stabilities are excellent and thermal stability is high. Further, the partial fluorine-based polyelectrolyte membrane has advantages of both a hydrocarbon-based polyelectrolyte membrane and a fluorine-based polyelectrolyte membrane because a cation transport functional group is attached to the ends of a fluorine-based chain similarly to a fluorine-based polyelectrolyte membrane.
When operated under low humidity conditions, a fuel cell and/or a redox flow battery have/has various advantages in that reactivity of a positive electrode is improved, and a hydroplaning phenomenon and contamination of a catalyst are lowered, and the like. However, a generally used polyelectrolyte membrane has a problem in that the battery performance rapidly deteriorates because physical properties such as cation conductivity are decreased under low humidity conditions. Therefore, there is a need for studies to solve the above-mentioned problems.